Molecular and Cellular Basis of PCB Developmental Neurotoxicity

描述（由申请人提供）：有相当多的公众和监管机构担心多氯联苯（PCB）的发育暴露会导致儿童严重的认知和行为缺陷，但评估这些化合物带来的风险一直很困难，因为PCB对发育中的神经系统影响的生物学机制尚未确定。我们最近证明，啮齿类动物在发育过程中暴露于商业PCB混合物中，会损害体内树突生长和可塑性，同时也会损害空间学习能力。这些对神经发育和认知功能的影响与中枢神经系统中ryanodine受体（RyR）的表达和功能改变有关。RyR调节钙依赖性信号通路，这些信号通路与活动依赖性树突生长有关，树突生长是发育中的大脑神经元连接的关键决定因素。本研究的目的是通过验证非共面多氯联苯通过破坏RyR功能改变树突生长和可塑性的假设，来表征多氯联苯发育神经毒性的机制和构效关系（SAR）。具体目标是：1。在体内测试RyR扰动和甲状腺激素缺陷在PCB对树突生长和可塑性影响中的相对贡献；2. 利用海马神经元原代培养，鉴定多氯联苯对树突生长影响的分子机制；3. 确定非共面多氯联苯如何改变培养海马神经元中钙释放单位蛋白质的功能和表达；4. 确定遗传突变ryr1和ryr2是否会增加人类对卤化化合物的敏感性，从而增加表达这些突变的小鼠对多氯联苯发育性神经毒性的易感性。这些研究解决了更好地理解多氯联苯发育神经毒性机制的关键需求。研究结果将为确定暴露风险和开发暴露及其影响的生物标志物提供合理依据。由于RyR基因在人群中表现出大量的表达突变和多态性，支持RyR作为发育中的神经系统中多氯联苯的分子靶点的数据将为放大环境诱导的神经发育障碍的遗传易感性提供见解。多氯联苯是一种持久性的、广泛存在的环境污染物，有令人信服的证据表明，发育中的大脑接触多氯联苯会导致儿童出现学习和记忆问题。但是多氯联苯是如何造成这些影响的还不太清楚。拟议研究的目标是将已知的多氯联苯的分子效应（激活ryanodine受体）与大脑发育的特定变化（破坏树突生长）联系起来。建立这种联系将为预测209种可能的多氯联苯中哪一种对发育中的大脑构成最大风险提供强有力的手段，并可能为放大环境诱发的神经发育障碍的遗传易感性提供新的见解。

DESCRIPTION (provided by applicant): There is considerable public and regulatory concern that developmental exposures to polychlorinated biphenyls (PCBs) cause significant cognitive and behavioral deficits in children, but assessing the risks posed by these compounds has been difficult because the biological mechanisms underlying PCB effects on the developing nervous system have yet to be identified. We have recently demonstrated that developmental exposure of rodents to a commercial PCB mixture impairs dendritic growth and plasticity in vivo coincident with deficits in spatial learning. These effects on neurodevelopment and cognitive function correlate with altered expression and function of ryanodine receptors (RyR) within the central nervous system. RyR regulate calcium-dependent signaling pathways that have been implicated in activity-dependent dendritic growth, which is a critical determinant of neuronal connectivity in the developing brain. The goal of our study is to characterize the mechanisms and structure-activity relationship (SAR) of PCB developmental neurotoxicity by testing the hypothesis that non-coplanar PCBs alter dendritic growth and plasticity by disrupting RyR function. The specific aims are to: 1. Test the relative contributions of RyR perturbation and thyroid hormone deficits in PCB effects on dendritic growth and plasticity in vivo; 2. Use primary cultures of hippocampal neurons to identify the molecular mechanisms mediating PCB effects on dendritic growth; 3. Determine how non-coplanar PCBs alter the function and expression of proteins that comprise calcium release units in cultured hippocampal neurons; 4. Determine whether heritable mutations in ryr1 and ryr2 that increase sensitivity to halogenated compounds in the human population increase susceptibility to PCB developmental neurotoxicity in mice expressing these mutations. These studies address the critical need to better understand mechanisms underlying PCB developmental neurotoxicity. Results will provide a rational basis for characterizing exposure risks and developing biomarkers of exposure and effect. Since RyR genes exhibit a significant number of expressed mutations and polymorphisms in the human population, data supporting RyR as a molecular target of PCBs in the developing nervous system will provide insights into genetic susceptibilities that magnify environmentally induced neurodevelopmental disorders. Polychlorinated biphenyls (PCBs) are persistent, widespread environmental contaminants, and there is compelling evidence that exposure of the developing brain to PCBs can cause learning and memory problems in children. But how PCBs cause these effects is not well understood. The goal of the proposed studies is to link known molecular effects of PCBs (activation of ryanodine receptors) to specific changes in brain development (disruption of dendritic growth). Establishing this link will provide a powerful means for predicting which of the 209 possible PCBs present the greatest risk to the developing brain and may provide novel insights into genetic susceptibilities that magnify environmentally induced neurodevelopmental disorders.